アルファ値付きの描画

#include "sptk.h"

#define WIDTH  300
#define HEIGHT 300

SPTK_IMAGE *winimg;
SPTK_IMAGE32 *layerimg,*blendimg;

SPTK_POINT start,last;
SPTK_RECT boxrc;

int drawcol_no = 0;
SPTK_PIX_RGBA drawcol[3] = {
    {b:255,0,0,128:b}, {b:0,255,0,128:b}, {b:0,0,255,128:b}
};

/** 点を打つ */

void drawlayer_pixel(int x,int y,SPTK_PIX_RGBA *pix)
{
    SPTK_PIX_RGBA *pd;
    double dstA,srcA,newA;
    
    pd = sptk_image32_getptbuf(layerimg, x, y);
    if(!pd) return;
    
    /* アルファ値 */
    
    srcA = pix->a / 255.0;
    dstA = pd->a / 255.0;
    
    newA = srcA + dstA - srcA * dstA;
    
    pd->a = (uint8_t)(newA * 255 + 0.5);
    
    /* RGB */
    
    if(pd->a)
    {
        pd->r = (uint8_t)((pix->r * srcA + pd->r * dstA * (1 - srcA)) / newA + 0.5);
        pd->g = (uint8_t)((pix->g * srcA + pd->g * dstA * (1 - srcA)) / newA + 0.5);
        pd->b = (uint8_t)((pix->b * srcA + pd->b * dstA * (1 - srcA)) / newA + 0.5);
    }
}

/** 四角形塗りつぶし */

void drawlayer_fillbox(SPTK_RECT *rc,SPTK_PIX_RGBA *pix)
{
    int ix,iy;
    
    for(iy = rc->y1; iy <= rc->y2; iy++)
    {
        for(ix = rc->x1; ix <= rc->x2; ix++)
            drawlayer_pixel(ix, iy, pix);
    }
}

/** 画面を更新 */

void update_screen(SPTK_RECT *updaterc)
{
    SPTK_RECT rc;
    int w,h;
    
    /* 更新範囲 */
    
    if(updaterc)
        rc = *updaterc;
    else
    {
        rc.x1 = rc.y1 = 0;
        rc.x2 = WIDTH - 1;
        rc.y2 = HEIGHT - 1;
    }
    
    if(sptk_rect_clip_wh(&rc, WIDTH, HEIGHT)) return;
    
    /* 合成 */
    
    w = rc.x2 - rc.x1 + 1;
    h = rc.y2 - rc.y1 + 1;

    sptk_image32_fill_plaid(blendimg, rc.x1, rc.y1, w, h);
    sptk_image32_blend_normal(blendimg, layerimg, rc.x1, rc.y1, w, h);
    
    /* ウィンドウ更新 */
    
    sptk_image32_blt_image(blendimg, rc.x1, rc.y1, w, h, winimg, rc.x1, rc.y1);
    sptk_update_rect(NULL, &rc, 0);
}

/** boxrc に矩形範囲をセット */

void set_boxrc()
{
    boxrc.x1 = start.x;
    boxrc.y1 = start.y;
    boxrc.x2 = last.x;
    boxrc.y2 = last.y;
    
    sptk_rect_swap(&boxrc);
}

void draw_xorbox(int time)
{
    sptk_image_box(winimg, boxrc.x1, boxrc.y1,
        boxrc.x2 - boxrc.x1 + 1, boxrc.y2 - boxrc.y1 + 1, SPTK_COL_XOR);

    sptk_update_rect(NULL, &boxrc, time);
}

void winhandle(SPTK_EVENT *ev)
{
    switch(ev->type)
    {
        case SPTK_EVENT_BTTDOWN:
            if(ev->mouse.btt == SPTK_MOUSEBTT_LEFT)
            {
                start.x = ev->mouse.x;
                start.y = ev->mouse.y;
                last = start;
                
                set_boxrc();
                draw_xorbox(2);
                            
                sptk_grab(NULL);
            }
            break;
        case SPTK_EVENT_BTTUP:
            if(ev->mouse.btt == SPTK_MOUSEBTT_LEFT && sptk_isgrab())
            {
                sptk_ungrab();
                
                drawlayer_fillbox(&boxrc, &drawcol[drawcol_no]);
                update_screen(&boxrc);
            }
            break;
        case SPTK_EVENT_MOUSEMOVE:
            if(sptk_isgrab())
            {
                draw_xorbox(-1);
                
                last.x = ev->mouse.x;
                last.y = ev->mouse.y;
                
                set_boxrc();
                
                draw_xorbox(2);
            }
            break;
    
        case SPTK_EVENT_WINDOW_KEYDOWN:
            if(ev->key.code == 'R')
                drawcol_no = 0;
            else if(ev->key.code == 'G')
                drawcol_no = 1;
            else if(ev->key.code == 'B')
                drawcol_no = 2;
            break;
        case SPTK_EVENT_WINDOW_CLOSE:
            sptk_quit();
            break;
    }
}

int main()
{
    sptk_init("test", WIDTH, HEIGHT);
    sptk_window_set_handle(winhandle);
    
    winimg = sptk_window_get_image();
            
    blendimg = sptk_image32_create(WIDTH, HEIGHT);
    layerimg = sptk_image32_create(WIDTH, HEIGHT);
    
    sptk_image32_clear(layerimg, NULL);
    
    update_screen(NULL);
    
    sptk_run();
    
    sptk_image32_free(blendimg);
    sptk_image32_free(layerimg);

    return 0;
}